I think its related to rockbox track numbers beeing 1 higher in some circumstances as it seems to happem when rockbox thinks track 1 is track 2 and you play 2nd last file rockbox thinks its the last track.

Video of it refusing to plat at www.guildwars.tyria.net/files/dump/rf.wmv

As for settings that vid was taken on a complete clean install of the latest build no settings applied apart from theme and eq.